Brazing alloy of copper, silicon, titanium, aluminum

ABSTRACT

A brazing alloy for brazing ceramics has the following composition, in weight percent: 1 to 4 silicon; 1 to 5 titanium; 0.5 to 6 aluminum; 89 to 96 copper.

This invention concerns a ternary brazing alloy of copper, silicon andtitanium for brazing ceramics. Such a ternary alloy is disclosed in U.S.Pat. No. 4,426,033 and European Patent Application 0 038 584. U.S. Pat.No. 4,426,033 discloses a ternary alloy containing 50 to 98.75% byweight of copper, 0.25 to 5% titanium, and from about 1% to about 45% ofa third metal selected from the group consisting of silicon, tin,germanium, magnanese, nickel and cobalt. EP application 0 038 584discloses a ternary brazing alloy containing 40 to 85 atomic % copper, 5to 60 atomic % titanium, 0 to 55 atomic % silicon.

A problem with the ternary brazing alloys disclosed in the abovereferences is the formation of oxidation product on the braze filletarea during the direct brazing of ceramic to metal.

I have found that if a controlled amount of aluminum is added to acopper, silicon, titanium brazing alloy of controlled composition, thatthe formation of oxidation product can be prevented or greatlyminimized. A brazing alloy as per this invention has a composition of,in weight percent, 1 to 4 silicon, 1 to 5 titanium, 0.5 to 6 aluminum,89 to 96 copper.

In the following examples, all compositions are expressed in weightpercent.

EXAMPLE 1

An alloy with a composition of 92.25% copper, 3.25% silicon, 2%aluminum, 2.5% titanium was tungsten arc melted on water-cooled copperhearth. The button was rolled down into 2 mil thickness foil.

The foil was placed between 1.2"×1.2"×0.060" thick alumina substrate andKovar strip 1/4" wide by 10 mil thick by 3" long. The assembly wasbrazed at 1050° C. under 10⁻⁵ torr vacuum. An excellent looking brazewas obtained. Pulling of brazed Kovar strip using Instron at 2 inch perminute resulted in 20 pound force peel which is an excellent strength.The alloy with a hardness of 138 Knoop hardness number met our hardnesscriteria. Kovar is an alloy of iron, cobalt and nickel made byWestinghouse Corporation.

An ASTM F-19 alumina tensile test piece was brazed with copper sandwich.That is, the assembly from bottom was alumina, 2 mil brazing alloypreform, 10 mil copper, 2nd brazing alloy preform and alumina. Ten setswere assembled and brazed to above schedule. All tested better than 10⁻⁹cc/second leak rate using He gas and helium mass spectrograph.

EXAMPLE 2

An alloy with a composition of 94.0% copper, 2.75% silicon, 1% aluminum,2.25% titanium was melted and peel test prepared as in Example 1. Anexcellent bright gold colored braze resulted. Peel test showed that 25pound force was required to pull off the Kovar tab from the aluminasubstrate.

EXAMPLE 3

As in Example 1, a button was prepared with a composition of 92.00%copper, 3.00% aluminum, 2.75% silicon, 2.25% titanium, and rolled into 2mil foil.

Peel tests were prepared and also hermeticity samples were prepared. Theassemblies were brazed under 10⁻⁵ torr vacuum and at 1050° C.

The peel test required 17 pound average pull on Kovar strip. The five(5) hermeticity test samples all passed the helium leak check.

EXAMPLE 4

An alloy with a composition of 90.25% copper, 5% aluminum, 2.25%silicon, 2.5% titanium was melted and rolled to 2 mil thickness foil asin Example 1. Peel test and hermeticity braze samples were prepared asin Example 1. It tested 16 lbs force to peel off Kovar from the aluminasubstrate. The hermeticity test showed that it met the 10⁻⁹ cc/sec. leakrequirement.

EXAMPLE 5

A powder admixture consisting of 97.75% minus 325 mesh atomized alloypowder, with a composition 94.12% copper, 2.81% silicon, 3.07% aluminumis mixed with 2.25% titanium hydride minus 325 mesh powder. Thiscombination results in a melted composition of 92.00% Cu, 3.00% Al,2.75% Si, 2.25% Ti. A screening paste consisting of 90% of aboveadmixture and 10% screening vehicle #235 from Ceramic Color Company wasprepared.

Using 105 mesh screen, with the screen placed 0.050" above1.2"×1.2"×0.060" thick alumina substrate as a snap off distance, theprepared paste was screened on to the alumina substrate and measuredabout 4 mil thick, dried, which is equivalent to 2 mil foil. Threestrips of Kovar peel test strips, measuring 0.25"×3"×0.010" thick wereplaced over coated alumina substrate. The assemblies were brazed at1050° C.×10 minutes under 10⁻⁵ torr vacuum furnace. The brazed layersbetween the strips were pin hole free.

The peel test resulted in 17 pound force to peel off the Kovar strip,which is equivalent to moly-metallized ceramic system.

In the following table, alloy compositions within this invention are inweight percent.

    ______________________________________                                        Composition                                                                   Sample                                                                              Cu     Al    Si   Ti   Liquidus                                                                             Solidus                                                                             KHN   Peel                          ______________________________________                                        83-13 94.00  1.0   2.75 2.25 1035   994   114   25                            65-13 92.50  2.0   3.50 2.0  1000   967   140   11                            65-16 92.25  2.0   3.25 2.50 1010   975   138   20                            65-10 93.50  2.0   3.00 1.50 1021   983    13                                 65-18 93.0   2.0   2.50 2.50 1036   995   115   18                            83-16 93.75  2.0   2.00 2.25 1049   1003  101   20                            65-2  91.25  3.0   3.25 2.50 1009   956   160   14                            65-G  92.00  3.0   3.00 2.00 1013   968   144   15                            65-3I 92.00  3.0   2.75 2.25 1012   978   130   17                            65-03 91.25  4.0   2.25 2.50 1022   990   148   14                            65-04 90.25  5.0   2.25 2.50 1019   985   150   16                            65-05 90.25  6.0   1.25 2.50 1032   1003  139   13                            ______________________________________                                    

In the table, KHN is the Knoop hardness. Liquidus and solidustemperatures are in degrees Centigrade. Peel is the average peelstrength in pounds.

I claim:
 1. A brazing alloy for brazing ceramics having the followingcomposition, in weight percent: 94 Cu, 2.75 Si, 1 Al, 2.25 Ti.
 2. Abrazing alloy for brazing ceramics having the following composition, inweight percent: 92.25 Cu, 3.25 Si, 2 Al, 2.5 Ti.
 3. A brazing alloy forbrazing ceramics having the following composition, in weight percent: 92Cu, 2.75 Si, 3 Al, 2.25 Ti.
 4. A brazing alloy for brazing ceramicshaving the following composition, in weight percent: 90.25 Cu, 2.25 Si,5 Al, 2.5 Ti.